Hybrid vehicles (hereinafter also referred to as “HV”) mounted with an engine and a motor as power sources are known. HVs are provided with a DC power supply such as a rechargeable secondary cell. HVs drive the motor by electrical power supplied from the DC power supply. In this case, in order to improve running performance of the vehicle, a boost converter may be used as a boosting device which boosts the DC voltage from the DC power supply and supplies the boosted voltage to the motor.
A boost converter for an HV generally includes a reactor and power switching elements such as IGBTs. The reactor includes a reactor core in which two or more core members made of magnetic materials are successively arranged via intervening gaps to form an annular shape, and coils which are wound around the core members. In a reactor constructed in such a manner, a chopper boosting operation is performed in which electrical energy supplied from the DC power supply is temporarily stored as magnetic energy in the reactor cores and discharged, by controlling ON and OFF states of the switching elements in a high-speed cycle.
As a conventional art document related to a reactor described above, for example, JP 2006-237030 A (hereinafter referred to as “Patent Document 1”) discloses an iron core with an object to provide a core having an easy axis of magnetization along the direction of a magnetic path over the entire region and capable of being constructed from a minimum number of required iron core strips without dividing the core strips for every linear region. This iron core is constructed from a pair of U-shaped iron core strips, each of which has an easy axis of magnetization along the magnetic path. Each iron core strip is constituted by laminating two or more oriented electromagnetic steel plates in a direction perpendicular to the easy axis of magnetization. The iron core strip is made up of three iron core portions successively positioned in the direction of the easy axis of magnetization. The adjacent two iron core portions are connected to each other at a coupling portion located at an end portion on an outer peripheral side of the U-shaped magnetic path. End surfaces which are formed in a direction perpendicular to the easy axis of magnetization at an end portion of the easy axis of magnetization of both of the adjacent iron core portions are arranged to face each other in such a manner that the easy axes of magnetization of both of the iron core portions are successively arranged along the magnetic path.
Further, as another conventional art document, JP 2009-71248 A (hereinafter referred to as “Reference 2”) discloses a reactor with an object to reduce copper loss and describes, as the most suitable structure, a magnetic core structure of a composite magnetic reactor core in which a ferrite magnetic core and pressurized powder magnetic core are combined. This reactor is an annular reactor made up of two ferrite magnetic core joints opposing each other, two or more magnetic core length portions which are arranged between the magnetic core joints and composed of pressurized powder body made up of soft magnetic powder and resin, and coils wound around the core length portions. The magnetic core length portions are constructed from two or more blocks which are successively arranged via intervening gaps. The intervening gaps are positioned on the inner side of the coils.